tbergdall:  I do not see any similarity between your Krag .22 and the "Sub-Caliber Rifles" that were training devices, made from Krag actions and .30 cal. barrels, that attached to Deck Guns and artillery pieces to allow cheap practice and training for Gun Crews.  Prior to 'becoming a .22', your rifle may have had alterations to allow its use with a "Sub-Target Rifle Machine".  This device allowed practice without ammo and mechanically marked a miniature target with a spring-loaded pointer.  The holes in your stock and the 'lobe' on the striker may have no relation to its use as a .22 rifle.

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